The present invention relates to a security element, for securing security papers, value documents and other data carriers, having a lenticular image that displays, from different viewing directions, at least two different appearances. The lenticular image includes a lens grid, composed of a plurality of microlenses, and a laser-sensitive motif layer that is arranged spaced apart from the lens grid, and the laser-sensitive motif layer comprises, in two or more motif layer sub-regions, different markings that are introduced by the action of laser radiation and that, when the motif layer is viewed with the lens grid, produce the at least two different appearances. The present invention also relates to a method for manufacturing such a security element, and a data carrier that is equipped with such a security element.
For protection, data carriers, such as value or identification documents, but also other valuable articles, such as branded articles, are often provided with security elements that permit the authenticity of the data carrier to be verified, and that simultaneously serve as protection against unauthorized reproduction.
Security elements having viewing-angle-dependent effects play a special role in safeguarding authenticity, as these cannot be reproduced even with the most modern copiers. Here, the security elements are furnished with optically variable elements that, from different viewing angles, convey to the viewer a different image impression and, depending on the viewing angle, display for example another color or brightness impression and/or another graphic motif.
In this connection, it is known to provide the data carriers with laser-engraved tilt images for safeguarding. Here, two or more different markings, for example a serial number and an expiration date, are laser-engraved in the data carrier at different angles through an arrangement of cylindrical lenses. The laser radiation here produces a local blackening of the card body, which makes the engraved markings visually visible. When viewed, depending on the viewing angle, only the respective marking engraved from that direction is visible such that, by tilting the card vertically to the axis of the cylindrical lenses, an optically variable tilt effect is created.
In addition to tilt images, also other security elements are known in the background art that present to a viewer direction-dependently different depictions in that corresponding micro-image elements are enlarged with the aid of microlenses, for example so-called moiré magnification arrangements and other micro-optical depiction arrangements.
In all of these security elements, the structuring of the micro-images is often technically more challenging than the structuring of the lenses, since a significantly higher resolution is required for the micro-images, especially since the image information for at least two views must be provided under each lens. Further, the line screens of the lenses and micro-images must match each other very precisely, since otherwise, in tilt images, for example, multiple views will be visible simultaneously, or in moiré magnification arrangements, image distortions can occur.
It is known to produce micro-images by means of printing methods, embossing methods, or by overlaying the images through the microlenses by means of a laser. Here, advantage is taken of the fact that an incident laser beam is focused by the microlenses, as a result of which, on the one hand, the required high resolution can be achieved, and on the other hand, the inscribed information is later visible also from the direction from which it was overlaid with the laser beam.
If one would like to implement such an overlaying by laser on an industrial scale, especially on a foil web in a roll-to-roll process, then numerous micro-images must be overlaid very quickly with very powerful lasers. Here, the laser beam is permitted to impinge on the foil having the lenses only at those sites at which, in the depiction produced, the image is later to be produced, so for example at which a metal layer is to be ablated. For this purpose, the laser beam can be scanned over the lens foil accordingly such that only the desired motif region is impinged on. Alternatively, the motif region can be defined with a mask that prevents, in some regions, the exposure of the underlying lenses.
In practice, however, both methods are quite complex. Suitable scanning devices are expensive and often do not achieve the speeds required in an industrial production line. In a roll-to-roll process, a mask should preferably move at the speed of the foil web, and moreover, a separate mask is needed for each view such that, in practice, the mask cannot simply be printed on the foil web. Alternatively, a separate printing step must be carried out for each view, the printing mask having to be removed after laser exposure from the appropriate direction.